Composite piston and method of making same



Dec. 9, 1941. J. w. SHOCK 2,265,873. COMPOSITE PISTON AND-METHOD 0F MAKING SAME Filed Sept. 12, 1938 INVENIUR. JACOB w. nooK BY RA/44A "Mm W ATTORNEYS.

Patented Dec. 9, 1941 COMPOSITE PISTON AND IWETHOD OF MAKING SAME Jacob W. Shook, Bellefonte, Pa, assignor to Titan Metal Manufacturing Company, a corporation of Pennsylvania Bellefonte, Pa,

Application September 12, 1938, Serial No. 229,595 .2 Claims. (01. 22-203) This invention relates to the production of composite metal articles, and more particularly to the production of an article of this type having one part formed by a forging or drawing operation and another part formed by casting. The invention is primarily and specifically directed to pistons for employment in valve devices forming a part of air brake systems, and has a special utility in connection with such devices.

It is well known that a forged or drawn metal article may possess physical properties not found in a cast metal article. However, due to the nature of a forging or drawing operation limitations as to the configuration of the article are imposed which are not encountered in a cast article.

I have devised a method of forming a com: posite article, partially forged and partially cast, wherein the desirable characteristics of a forging as to wear, relative imperviousness to fluids, and strength are achieved and the parts not practically susceptible of forging are cast resulting in an integral article not practically produceable by either forging or casting alone. I have hereinafter illustrated my invention as embodied in a piston, preferably formed of copper-zinc alloy metals, but it is understood that it is equally adaptable to various other metal articles, although I claim a specific utility for the'invention in this form.

In the hereinafter described piston I employ brasses of the Munz metal type although the forged part is possessed of different physical properties and of diiferent composition than the die cast part. Since the forged piston part is substantially non-porous it has a greater strength, greater elongation, greater yield point and a greater resistance to fatigue and shock than the die cast part. Additionally, I preferably employ a greater amount of lead in the forged part which together with the non-porous nature thereof renders the forged part easier of machining than the die cast part.

It is a primary object of my invention to produce a composite metal article having one part thereof forged and another part cast.

Another object; of my invention is to provide a unitary metal article having parts thereof possessing difierent physical characteristics.

Another object of my invention is to provide a method of forming an article partially by forging or drawing and partially by casting.

Another object of my invention is to provide an improved method of forming a piston of a special design for use in valve devices forming a part of an air brake system.

Other objects of my invention and the invention itself will become increasingly apparent from a consideration of the following description:

'Figure 1 is an end elevational view of a piston head which I may employ;

Figure 2 is a side elevational view of the piston head of Figure 1;

Figure 3 is a longitudinal medial section through a piston head and shank integrally joined; and

Figure 4 is a section along line 44 of Figure 3.

Referring now .to the drawing I have indicated the piston head generally at I0 and the shank at I Lthe head comprising a circular flange l2 and an axially extending stem [3. The face of the flange is preferably recessed as indicated at M and the flange or web l2 terminates in an annular portion thickened in an axial direction in' order that a packing ring groove may be cut at the point 15. 'The stem l3 comprises a generally frustro-conical portion [6 extending to a reduced portion Il forming a'shoulder [8 therebe'tween. Portion I! has a groove i9 cut therein adj acent' an enlarged end. 20.

As best illustratedin' Figures 2 and 4, the end 20 is splined or provided with. circumferentially spaced and axially extending grooves as indicated at 2 I.

The head ii] is preferably formedof brass or a copperzinc alloy which maybe drawn or forged in any well known manner but preferably on a crank press. The excess flash metal is then trimmed from the forging after which it may be treated in a pickling bath. The groove I9 is then cut in stem l3 and also the packing ring groove at E5 in flange l2 if desired. The groove 1 9 and grooves 2'! are provided to form an interlocking connection with the shank l I preventing any tendency toward relative axial or rotary movement between the shank and head and I contemplate that any other suitable connection may be used such as forming threads on stem 13.

The shank I l is preferably die cast and is formed of substantially the same material as the head. The brass or copper-zinc alloy is melted and transferred toaholding furnace preparatory to being forced into the die under pressure in a well known manner. The head i0 is disposed with the stem I3 in the die cavity whereby'the shank metal indicated at 22 may encircle stem I3 flowing into groove l9 and 2| to form an interlocking connection. The shank metal at 22 forms a circular flange abutting shoulder l8 and form- .It will be apparent that the shank II is not properly susceptible of being formed by forging but can be economically die cast. Die casting the shank l l or casting under pressure decreases the porosity of the metal and insures a firm bond between the shank and head. The piston is adapted to be used with fluids such as air under considerable pressure and the head must be relatively non-porous as will be more fully explained presently, Forged metal is less porous than pressure cast metal and more suitable for machining in that porosity occurs in pressure casting which is disclosed when the cast surface is machined.

The integrally joined shank and head are removed upon opening the die and the piston is inspected, trimmed, machined, pickled in part or subjected to any desired finishing operations.

I have previously explained that while brasses of the Munz metal type are used in making my improved composite die cast and forged article the two brasses differ relatively both in physical and chemical properties. A typical example of compositions employed are as follows:

Composition of brass of die cast part Percent Copper 59.00 to 62.00 Tin .25 to.'75 Iron "maximum" .15 Manganese maximum .10 Silicon maximum .20 Aluminum maximum. .15 Lead .50 to 1.50 Zinc remainder Composition of brass of forged part Percent Copper 58.00 to 61.00 Tin maximum .10 Iron maximum .15 Lead .50 to2.00 Zinc remainder In the foregoing detailed description I have described my invention in terms of a device of rather general application. I now wish to refer to the specific field of application of the invention and to the special utility possessed by it in practice in that field,

In a particular form of air brake valve device which is part of a brake equipment now standard on every American railroad, and known as the AB brake equipment, it was formerly the practice to make the main operating pistons of cast meial. This standard valve device is fully described and claimed in United States Patent N0. 2,031,213, granted February 18, 1936 to Clyde C. Farmer. The cast piston head and stem were then machined to final shape and size. One of these machining operations involved the cutting of a rather deep groove at l5 for the purpose of receiving a metallic packing ring of rectangular cross section. It will be observed that the bulk of the metal at this point is greater than in the flange or web portion and because of this many blow-holes resulted during the casting operation. Because of the presence of these blowholes it was diificult to accurately machine a groove of uniform width and depth. As a consequence, when a packing ring was mounted in an irregular groove it would not move radially therein with the freedom required for it to provide the necessary seal with the piston bushing.

Now the operating conditions in the standard valve device referred to are such that the pistons must be capable of making small predetermined movements in response to low differential pressures acting thereon. When the packing ring was faulty in its operation due to sticking or bindin in its groove the low differential pressures would sometimes not properly operate the piston.

After considerable experimentation I discovered that it was possible to make a piston and shank of the peculiar shape illustrated in the drawing according to the teachings hereinbefore set forth. Pistons made according to these teachings were found to be free of the difliculties attending the all-cast piston. This is believed to be due to the fact that with the piston head formed by forging, the porosity of the metal in the region where the packing ring groove is cut is so slight as to no longer be of any importance.

The invention has been applied to many pistons which have been installed in a very large number of AB valve devices now operating in daily service. The invention has successfully solved the problem which formerly existed in these valve devices in connection with all-cast pistons.

What I claim is:

1. The method of making a composite piston having a forge head and a cast shank extending in an axial direction therefrom, for use in an air brake valve device, which comprises forging from a blank of copper-zinc alloy a head having an axially extending stem and a Web portion extending radially outwardly therefrom and terminating in a relatively thickened annulus, shaping the periphery of said stem adjacent the free end thereof into an irregular contour, mounting the forged head in a die with the stem extending into the die cavity, flowing copper-zinc alloy metal into the die cavity under pressure and causing it to encircle in intimate and interlocking contact with the stem, and removing the thus integrally joined shank and head from the die.

2. A composite piston for use in an air brake valve device, comprising in combination, a head forged from copper-zinc-lead alloy and having an axialiy extending stem portion and a Web portion extending radially therefrom and terminating in a thickened annular portion in which a packing. ring groove may be machined, said stein portion having part of its peripheral surface of irregular contour, and a shank formed of pressure die cast copper-zinc alloy encircling said stem and having intimate and interlocking contact with the said irregular surface thereof, whereby the shank and head are integrally joined together.

JACOB W. SHOOK.

CERTIFICATE OF CORRECTION. Patent No. 65 875- December 9, l9hl.

JACOB W. SHOCK- It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page '2, second column, line Lil, claim 1, for "forge" read '--forged--; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5rd day of February,A. D. l9L|.2.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

